Rapid thermal processing (RTP) is any thermal processing technique that allows rapid heating and rapid cooling of a substrate such as a silicon wafer. The specific peak temperature and heating time used depend on the type of wafer processing. RTP wafer processing applications include annealing, dopant activation, rapid thermal oxidation, and silicidation among others. The rapid heating to relatively high temperatures followed by the rapid cooling that characterize RTP provides more precise wafer processing control. The trend for thinner oxides used in MOS gates has led to requirements of oxide thicknesses less than 100 Angstroms for some device applications. Such thin oxides require very rapid heating and cooling of the wafer surface in an oxygen atmosphere to grow such a thin oxide layer. RTP systems can provide this level of control, and are used for rapid thermal oxidation processing.
A result of the short heating cycle used in RTP is that any temperature gradients that may exist across the wafer surface can adversely affect wafer processing. It is, therefore, desired in RTP to monitor the temperature across the wafer surface and improve temperature uniformity in and on the wafer surface during processing. As a result, the placement, control, and monitoring of individual heating elements is designed so that the heat output can be controlled to help improve temperature uniformity across the wafer surface.
However, current approaches will not usually produce the temperature uniformity needed. Variation in heat intensity due to element failure or poor performance can greatly compromise the desired temperature profile control and result in unacceptable process results. Accordingly, a monitoring system that can detect failure or unacceptable element performance during wafer processing is a useful feature for an RTP system.
Therefore, there is a need for an improved apparatus and method for heating element failure detection. Further, a failure detection system that is independent of voltage and current waveforms is needed. A failure detection system that can identify which element has failed is also needed.